Hypersonic plasma thermocouple



p 1965 T. P. COTTER 3,206,624

HYPERSONIC PLASMA THERMOCOUPLE Filed Aug. 31, 1961I[/III/I//IIIIIIIII/II/IIII[IIIIIII///I///I/III/ IIIII/II/IIII7////0 ,AIII[li/IIIIII,,III/llIIIIIIIIIIII/I,IIIIIIIIIIIIIIIIIIIIIIIIIlil/,IIIIIIII W/T/VESSESJ INVENTOR. Bz'hedore P. Coffer United States Patent O3,206,624 HYPERSONIC PLASMA THERMOCOUPLE Tleodore P. Cotter, Los Alamos,N. Mex., assignor to the United States of America as represented by theUnited States 'Atomic Energy Commission Filed Aug. 31, 1961, Ser. No.135,381 4 Claims. (CI. 310-4) The present invention relates to a verysimple direct current electrical power supply applicable to a vehiclemoving in an ionized medium. The hypersonic plasma thermocouple of thepresent invention is an application of the basic phcnomenon of thedevelopment of a substantial thermal in a gaseous plasma which issupporting a temperature gradient. The principle is applicable to :anyvehicle which is moving in any gaseous medium with a sufficiently highvelocity as to create and maintain a region of ionized plasma ofnon-uniform temperature in its vicinity.

An object of the present invention is to provide a simple, low voltage,high direct current, electrical power supply for use by a reentry orother hypersonic vehicle.

It is a further object of the present invention to provide methods andmeans for converting the heat energy developed by a reentry vehicle intoelectrical energy to operate an electrical load carried by the vehicle.

A further object of the present invention is to provide methods andmeans of utilizing a portion of the normally dissipated heat energydeveloped by a vehicle which is moving in any gaseous medium with asufliciently high velocity to create and maintain :a region of ionizedplasma of non-uniform temperature in its vicinity.

The mechanism of heat transfer and hypersonic flow over a body is wellknown, see for example, chapters 12 and 13 of Space Technology, editedby H. Seifert and published by John Wiley & Sons, Inc.

Every conducting medium may be characterized by its relativethermoelectric power, a quantity expressed in units of potentialdifference per degree temperature difference. In metals, thethernoelectric powers are of the order of one microvolt per degreecentigrade. These low values are commonly attrbuted to the fact that theelectron gas in a metal is degenerate, i.e., the electron energydistribution is almost independent of temperature. In non-degeneratemedia, such :as the electron clouds in a vacuum, in a plasma, in asemiconductor or an electrolyte, the characteristic value of thethermoelectric power is about 1000 times as great, or more nearly amillivolt per degree centigrade.

The present invention and the results produced thereby can be moreclearly understood by reference to the :attached drawings, herebyincorporated by reference, in

which- FIGURE l is a vertical cross section of a model simulating thepossible appearance of the forward end of a vehicle incorporating thehypersonic plasma thermocouple of the present invention,

FIGURE 2 is a vertical cross section of a second additional embodimentof the invention,

FIGURE 3 is a vertical cross section of a third additional embodiment ofthe invention,

FIGURE 4 is a vertical cross section of a fourth additional embodimentof the invention, and

FIG. 5 is a vertical cross section of a fifth additional embodiment ofthe invention.

Near or at the forward end of the vehicle a refractory electricallyconducting thermionic emitter is placed so as to be in contact with theionized medium surrounding the vehicle. Further back along the vehicle,and separated from the emitter by an electrical insulator, is placed anelectrically conducting collecting electrode, which is also 3,206,624Patented Sept. 14, 1965 'ice in contact with the surrounding ionizedmedium. The existence of a temperature difference between the emitterand collector regions will give rise to an electromotive force of somefew volts, from which source it is possible to draw very large Currents.An electrical load may now `be connected internal to the vehicle betweenthe emitter and collector, and may be operated by this power supply.

Since the thermoelectric power of plasma in general is of the order ofone millivolt per degree centigrade, and since it should be possible toobtain temperature differences of at least a thousand degrees centigradebetween the emitter and collector regions, it is reasonable to expectthe device to develop one or more volts of potential difference. Ofcourse, there will be additional dependence of the voltage on the Workfunctions of' the particular emitter and collector materials chosenl Theamount of current which may be drawn from the device will dependprimarily upon the electron emission characteristics of the emitter, thegeornetry of emitter and collector, and the electrical resistance of theplasma. With suflicient collector area and favorable location, and withadequate ion density in the plasma, one might expect to draw manyamperes per square centimeter of emitting surface, for a wide variety ofpossible emitter materials. The electrons will fiow from the emitter tothe collector through the external plasma, so that regarded as a powersupply, the emitter would be the positive terminal of the device.

A series of five models was prepared, in order to simulate the possibleappearance of the forward end of a vehicle incorporating a hypersonicplasma thermocouple power supply. A Giannini Plasmatron with a A3"diameter throat, Operating at 35 kilowatts input power, operating oneither argon or an argon-air mixture, was used as a source of hotplasma.

The very simple structure of a device for use in carrying out thepresent invention is shown in five modifications in FIGURES 1 5. Themain elements of such a device are the emitter electrode 1 placed at theforward end of the device, the collector electrode 2 placed further backalong the device, and the electrical insulation sleeve 3 in FIGURES 1and 2, and sprayed layer 5 in FIGURES 3, 4,'and` 5. The leading edges of'the vehicle are illustrated in FIGURE 5 at 7. This representation ofthe leading edges is, of course, for the purposes of illustration, theonly criterion as to the location being that it is desirable to placethe emitter electrode 1 near the forward end of the device. The emitterand collector electrodes may be of the same material. The only criterionis that they be electrically conductive. FIGURES 3, 4, and 5 haveadditional element 6 which acts merely as a spacer and may be of thesame material as the emitter and collector electrodes. In the testsreported below both electrodes were composed of Graphitite-G, a graphitemanufactured by Graphite Specialties, Inc. The electrical insulation maybe of any type, the material used in said tests was porcelain in FIGURES1 and 2 and sprayed layers, .01 to .02 inch thick, of aluminum oxide inFIG- URES 3, 4, and 5.

The electrodes may be connected to an electrical load in any knownmanner. In FIGURES 1 and 2 the electrical lead 4 was tungsten, and inFIGURES 3, 4, and 5 it was tantalum.

The models were placed in turn in the jet of the plasmatron with theiraxes parallel to the axis of the plasmatron jet. The electrical outputwas measured between the rear end of the collector afterbody and therear cmergent end of the electrical connection 4 which connects with theemitter tip. In the experiments with FIGURES 1 and 2 these terminalswere simply connected alternately with a voltmeter and an ammeterthrough a variable resistive load. For the experiments 3 with FIGURES 3,4, and 5, a two channel recording system was provided so that voltageand current could be obtained simultaneously and continuously.

Experimental results are given in the following table. In all cases,after an initial transent period of about a second, the emitter tipbecame and remained the positive terminal of the device, as expected.

From the table it is seen that the largest open circuit voltage, 3volts, was exhibited by FIGURES 1, 4, and 5. The largest short circuitcurrent, 6.8 amperes, was produced by FIGURE 4. The largest power, 4watts, was produced by FIGURE 1.

In the following table the model numbers 1 through 5 correspondrespectively with the embodiments shown in FIGURES 1 through 5 of thedrawing.

Performance of hypersonic plasma thermocouple models This invention isan extension of the basic phenomena of the development of a substantialthermal in a gaseous plasma which is supporting a temperature gradientas set forth and described in co-pending U.S. application Serial No.821,339, the subject matter of which is incorporated herein byreference.

It is, therefore, apparent that the present invention provides a novelplasma thermocouple utilizing a portion of the heat accompanying avehicle moving at hypersonic speeds in a gaseous atmosphere which hashitherto been dissipated. While presently preferred embodiments havebeen described, it is clear that many other modifications may be madewithout departing from the scope of the invention.

What is claimed is:

1. A hypersonic plasma thermocouple comprising a body portion mounted ona vehicle, said vehicle being capable of sufficent velocity through agaseous medium to ionize the gas adjacent said vehicle and said bodyportion, a refractory electrically conducting thermionic emitter placednear the forward end of the body in contact with the ionized gas at onetemperature, an electrically conducting collecting anode placed furtherback along the body in contact with the ionized gas at a lowertemperature, and an electrical insulator separating said emitter andsaid collecting anode, whereby an electrical load may be connectedbetween said emitter and sai-d collecting anode to be operated by thispower supply.

2. A hypersonic plasma thermocouple mounted on a vehicle, said vehiclebeing capable of sufficient velocity in a gaseous medium to ionze thegas adjacent the vehicle, said hypersonic plasma thermocouple comprisingan electrically conducting thermionic emitter placed in contact With theionized gas at one temperature, and an electrically conductingcollecting anode in contact with the ionized gas at `a lowertemperature, said enitter and anode separated by an electrical insulatorwhereby an electrical load may be connected between said ernitter andsaid collecting anode.

3. A hypersonic plasma thermocouple as in claim 2 Wherein the ernitterand collecting anode are of the same material.

4. A hypersonic plasma thermocouple as in claim 2 Wherein the gaseousmedium comprises air.

References Cted by the Examiner UNITED STATES PATENTS 2,5l0,397 6/50Hansell 310-4 X FOREIGN PATENTS 866,434 5/41 France.

OTHER REFERENCES Journal of the Aeronautical Sciences, April, 1958, page240.

ORIS L. RADER, Primary Exam'ner.

MILTON O. HIRSHFIELD, DAVID X. SLINEY,

Exam'ers.

2. A HYPERSONIC PLASMA THERMOCOUPLE MOUNTED ON A VEHICLE, SAID VEHICLEBEING CAPABLE OF SUFFCIENT VELOCITY IN A GASEOUS MEDIUM TO IONIZE THEGAS ADJACENT THE VEHICLE, SAID HPERSONIC PLASMA THERMOCOUPLE COMPRISINGAN ELECTRICALLY CONDUCTING THERMIONIC EMITTER PLACED IN CONTACT WITH THEIONIZED GAS AT ONE TEMPERATURE, AND AN ELECTRICALLY CONDUCTINGCOLLECTING ANODE IN CONTACT WITH THE IONIZED GAS AT A LWER TEMPERATURE,SAID EMITTER AND ANODE SEPARATED BY AN ELECTRICAL INSULATOR WHEREBY ANELECTRICAL LOAD MAY BE CONNECTED BETWEEN SAID EMITTER AND SAIDCOLLECTING ANODE.